Fix latent API bug where multi-word fields (RecurrenceDuration, ParentUUID,
CreatedAt) serialized as PascalCase, breaking the frontend. Add explicit
snake_case json tags and custom MarshalJSON/UnmarshalJSON on Task, Status,
and APIKey to emit unix timestamps and string status codes.
Add Urgency float64 as a derived field on Task, populated via
PopulateUrgency helper in all handlers before serialization. The report
engine's sortByUrgency now also retains the computed score.
Frontend updated with urgency type, color-coded badge in TaskItem, and
mock data values.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
